Studies are planned to monitor purine metabolism of the myocardium during and after global ischemia on cardiopulmonary bypass in experimental animals. Serial core biopsies are taken for the determination of ATP, ADP, and AMP. Uric acid and allantoin are determined in blood. The prime objective of this proposal is to improve currently available myocardial preservation techniques by minimizing the loss of adenosine nucleotides and metabolites during global ischemia and restoring to normal levels after reperfusion by methods that appear to be effective in hemorrhagic shock. Allopurinol is administered prophylactically to inhibit the enzyme xanthine oxidase and thus prevent the irreversible loss of functional purines. 2-Ethylamino-1,3,4-thiadiazole is administered before global ischemia to increase the de novo synthesis of purines. A mixture of ATP and magnesium chloride is given prophylactically. Moderate hypothermia and cardioplegic arrest are used in these animals. The myocardial function is evaluated in separate groups of animals.